1. Field of the Invention
The invention relates to a method for structuring a flat substrate composed of glass material in the course of a viscous flow process, in which the glass flat substrate is joined to a surface of a flat substrate, preferably a semiconductor flat substrate, which has at least one depression bounded by a circumferential edge located in the surface and, in the course of a subsequent tempering process, is changed to a viscous free-flowing state in which at least proportions of the free-flowing glass material of the flat substrate flow over the circumferential edge into the depression in the flat substrate and furthermore to an optical component is described that can be manufactured with a method described above.
2. State of the Art
Manufacturing processes for manufacturing optical components which use silicon technology or wafer manufacturing make it possible to design miniaturized embodiments of optical or micro-opto-electro-mechanical systems (MOEMS), with the latter providing optical components as constituent elements of a housing component in so-called wafer level packages (WLPs). Such methods furthermore have great potential to save costs, because hundreds to thousands of components can be processed in parallel on a wafer. Moreover, in the joining of the optical components with micromechanical fastening structures supporting the aforesaid, there is no need to provide any joining tools or adjustment aids, in particular since the manufacturing processes inherently comprise mechanically very precise joining mechanisms.
Such a manufacturing method is, for example, described in EP 1 606 223 B1, which is based on the manufacture of optical surfaces based on the viscous flow of glass. To this effect a first wafer comprising a first glass type is connected to a second wafer comprising silicon or a second, higher-melting, glass type, e.g. by anodic bonding or direct bonding (fusion bonding). At its two planar surfaces the second wafer comprises depressions that provide a three-dimensional surface profile that as a result of the depressions includes structured cavities that are open on one side. While the planar surface regions after bonding are firmly connected to the first wafer, the cavities allow free flowing of the glass material of the first wafer as soon as said wafer in a tempering process at e.g. 700-800° C. has reached adequately low viscosity. During the free flowing of the glass into the cavities of the structured second wafer the forming of the surface of the first wafer is decisively determined by the surface tension of the glass. Thus, depending on the difference in the pressure between the deeply structured cavities and the atmosphere in the glass oven, concave or convex structures form on the surface of the first wafer, which surface faces the cavities.
Furthermore, the glass flow process is influenced by further factors, for example by the geometric design of the flowing front of the viscous glass material flowing into the cavities, and by the gas volume displaced by the material transport of the glass. The flow process stops as soon as equalization between the interior pressure and the ambient pressure has been reached, when the cavity is completely full, provided it has previously been evacuated, or when the viscosity of the glass material is no longer sufficient to support flowing. In the processing of glass the latter is the case, as a rule, if the process temperature drops to below a critical temperature value.
Apart from the use of glass, transparent polymers can also be used for producing optical components in the course of the above-described viscous flow process. If suitable polymers are selected, the viscosity can, for example, also be reduced in a controlled way by photo-induced chemical curing in order to in this manner achieve a flow stop.
In the hitherto known variations of the viscous flow process a two-dimensional structural plane is used for determining the basic shape of the optical component that is forming, while the height profile of the optical component results from process control. For example, optical lenses with a spherical profile can easily be manufactured in this way because the spherical shape results from a circular basic shape and a surface that is in force equilibrium. By including dynamic flow movements it is also possible to overlay so-called aspherical corrections, that in conical or hyperbolic components of the spherical basic shape.
The viscous flow process is particularly advantageous in the production of optical components with freely formable optical surfaces or of particularly smooth free-form surfaces that are used for impression forming, for example by means of embossing techniques, because no mechanical polishing or post-processing of the surfaces is required. Correspondingly, an already known use of the method relates to the production of a replication shape from a higher melting glass that, as described above, can be used as a second wafer for forming the first wafer. However, in order to form a three-dimensional structure, in free viscous flowing it is only the physical effects of surface wetting and surface tension that are available to a user.
EP 1 572 594 B1 discloses a method for post-processing optical lenses as described above, in which method elliptical areas of increased steepness in the transition region between the lens and the glass flat substrate can be removed by a thermal post-processing step supported by a moulding tool.
In contrast to this, the production of planar surfaces that are largely inclined in any desired manner and that can be used as mirrors or as optical prisms is problematic. Likewise, the production of surfaces that are inclined along any desired contour, that is surfaces in the form of an equiangular or oblique-angled coplanar pyramid segment, is not possible with the hitherto-known viscous flow process.
In reality, known manufacturing processes for creating projecting structures are based on replication processes such as moulding of lenses. In these glass impression techniques, due to the high operating temperatures involved, only those materials can be considered for mould construction that are capable of withstanding the high temperatures and pressures experienced. Nevertheless, such methods only allow the replication of small work pieces, but not of entire wafers. In the field of wafer technology, as a subtractive process diamond grinding with high-precision numerically controlled machines is used in order to create microstructured surfaces of almost optical quality. Ultrasonic processing and laser direct structuring are further alternatives in this context. By means of chemical post-processing, the surfaces can be smoothed to usually achieve adequate optical quality. Furthermore, chemical etching techniques exist that allow structuring of height profiles. Additive processes such as vapor deposition are rather rarely worth considering in the context of height profiles of several micrometers.